This invention is directed to an impeller for centrifugal pumps particularly for use in pumping of fluent media. More precisely, the invention is directed to an impeller of the so-called single vane type, which means that the impeller is provided with one single vane which goes helically around the impeller either partly or perhaps entirely. Cover discs are located at the helical edges of the vane and cooperate with it to form a channel.
Pump impellers of the type referred to are primarily used for pumping of liquids containing solid bodies, for instance, sewage water. The advantage of this configuration is that the risk of clogging decreases if only one vane is used. In some instances, a certain minimum thrulet in a pump impeller for sewage pumps is prescribed by Governmental regulation. Such thrulet can only be fulfilled by a single vane impeller if reasonable dimensions are maintained.
Previously known impellers of the single vane type have the vane formed of generally constant thickness between the cover discs and leading edge near the pump inlet to the trailing edge near the pump outlet. One such impeller of this type is shown in the Swedish published patent application No. 7,806,198-3.
Such impellers do have certain disadvantages. As the vane thickness is constant, the channel which is formed by the vane has a constant or sudden increasing cross-section from the inlet towards the direction of the pump outlet. This steady increase is most significant near the inlet. This rapid increase in cross-sectional area results in a rapid decrease in fluid velocity and local pressure which may cause an undesirable turbulence and possible cavitation. Additionally, an increased risk of solid body collection, especially at the leading edge of the vane exists which would result in a decreased cross-sectional area at that location causing increased probability of clogging and/or decreased pump efficiency. Any clogging of the impeller results in an increased load on the driving unit which sometimes triggers the overload protection devices resulting in work stoppage and requiring servicing of the pump.